PVC compositions are well known in the art (see, for example, U.S. Pat. No. 6,063,846, U.S. Pat. No. 6,608,142 and U.S. patent publication 2005/0203230). PVC compositions that do not contain a plasticizer tend to be rigid and are suitable for the manufacture of rigid products such as pipe and tubing. PVC compositions that include a plasticizer tend to be flexible and are suitable for use in such applications as wire and cable insulation and jacketing, and medical device components. Examples of PVC compositions containing a plasticizer include the FLEXALLOY® products available from Teknor Apex.
Plasticizers are compounds or mixtures of compounds that are added to polymer resins to impart softness and flexibility. Phthalic acid diesters (also known as “phthalates”) are well-known petroleum-derived plasticizers that are widely used in many flexible polymer products, such as polymer products formed from PVC and other polar polymers. Known petroleum-derived plasticizers also include trimellitates and adipic polyesters, both typically used in high temperature applications. Mixtures of plasticizers are often used to obtain optimum properties.
Petroleum-derived plasticizers, particularly the phthalate plasticizers, however, have come under intense scrutiny by public interest groups that are concerned about their negative environmental impact and potential adverse health effects in humans (especially children). As such, plasticizers derived from other sources have become of great interest, particularly those derived from biological sources such as seeds and nuts. Exemplary biological sources include, but are not limited to, oils derived from soy bean, linseed, tung seed, coconut, palm, olive, cotton seed, oiticica seed and castor bean. Plasticizers derived from biological sources are generally phthalate free. Bio-based plasticizers are advantageous because they help reduce greenhouse gas emissions, and enable the user to obtain carbon and/or LEED (Leadership in Energy and Environmental Design) credits. However, if conventional processes for producing a PVC dry blend use a bio-based plasticizer, it results in an overly dry powder blend having a low bulk density, e.g. <0.60 g/cc, with very poor output feed rates to a subsequent extruder or other processing apparatus, for example, an output rate in the range of 10-50 gm/minute for a single screw extruder of 0.75-inch (19 mm) barrel diameter with a 25:1 L:D general purpose polyethylene screw at 75 rotations per minute screw speed. If a conventional dry blending process for producing a PVC dry blend use a conventional phthalate plasticizer, it results in a dry powder blend having a high bulk density, e.g. >0.7 g/cc, with very good output feed rates to a subsequent extruder or other processing apparatus, for example, an output rate in the range of 65-75 gm/minute for a single screw extruder of 0.75-inch (19 mm) barrel diameter with a 25:1 L:D general purpose polyethylene screw at 75 rotations per minute screw speed. Consequently, a need exists for a process for producing dry blends of PVC and bio-based, phthalate-free plasticizers having the same, or substantially the same, chemical and/or physical properties as dry blends made from PVC and phthalate plasticizers.